Diabetes mellitus is the fastest growing diagnostic class in the cardiovascular and end stage renal disease population, accounting for almost half of all patients beginning dialysis. It is therefore a major health care problem. However the basic underlying mechanisms are not very clear. Emerging evidence strongly supports a role for free fatty acids and oxidized lipids in complications such as diabetic nephropathy (DN). Examining the mechanisms involved can provide critical information regarding the pathophysiology of complications associated with Type 1 and Type 2 diabetes. In the previous funding period, we identified key mechanisms Initiated by Angiotensin II (Ang II) and high glucose. In renal mesangial cells (MC) and also accumulated extensive evidence that these diabetic stimuli regulate the formation of oxidized lipids of the 12/15-lipoxygenase (LO) pathway of arachidonate metabolism both in vitro and in vivo. These lipids induced cellular hypertrophy, profibrotic and extracellular matrix genes in mesangial cells by regulating specific signaling pathways and transcription factors. We demonstrated in vitro and in vivo relevance to diabetes, DN, proteinuria and vascular dysfunction and made significant progress in understanding the signal transduction events involved. In this renewal, we will extend our studies based on new observations of novel cross-talk mechanisms by which the LO pathway interacts with growth factor signaling pathways to augment fibrotic gene expression. We will use novel gain- and loss-of-function approaches to examine how LO lipid products and diabetogenic agents mediate the pathogenesis of DN 1) by inducing the expression of fibrotic genes via novel nuclear transcriptomic events in MC;2) by orchestrating key oxidative and survival events in MCs;3) by playing key roles in the progression of DN in mouse models of type 1 and type 2 diabetes. Our overall hypothesis is that: Diabetes and insulin resistance lead to increased activity and expression of 12/15-LO in glomerular MCs and tills leads to key changes associated with both early and late stages of DN. This is a consequence of 12/15-LO mediation of growth factor and high glucose (HG) effects and augmented expression of profibrotic and cell survival related genes. Four Specific Aims will use state-of-the-art approaches to test the cellular, molecular and signal transduction mechanisms of actions of LO products, as well as, consequences of genetic overexpression, and knockdown with LO knockout mice or shRNA treated cells and mice. These integrated in vitro and in vivo studies are expected to provide new information on the pathology of glomerular disease in diabetes and also lead to the identification of novel new therapeutic targets.